Conventionally, an automated apparatus or an unmanned apparatus for detecting a condition of traffic congestion due to a road construction is proposed. That Is, for example, Japanese patent document JP-A-2002-49985 discloses a technique that determines a congestion time based on a travel time of a specific vehicle between two positions in the proximity of a construction section of a road in addition to the number of vehicles passing a certain point.
However, the above technique does not necessarily provide an accurate detection result because the congestion condition is estimated based on vehicle information that is derived only from a limited number of positions.